Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $211.38   8.442%   $229.2247   $229.22   $229.20   $229.20  
  Purchase #2 $100.69   13.178%   $113.9589   $113.96   $113.95   $114.00  
  Purchase #3 $197.47   10.473%   $218.151   $218.15   $218.15   $218.20  
  Purchase #4 $126.71   5.617%   $133.8273   $133.83   $133.85   $133.80  
  Purchase #5 $121.63   7.143%   $130.318   $130.32   $130.30   $130.30  
  Purchase #6 $109.91   3.728%   $114.0074   $114.01   $114.00   $114.00  
  Purchase #7 $88.93   6.434%   $94.6518   $94.65   $94.65   $94.70  
  7 purchase totals = $956.72       $1,034.1391   $1,034.14   $1,034.10   $1,034.20